The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 19953474.8, filed on Nov. 5, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a shoe press roll for dewatering a fibrous web, in particular a paper web, cardboard web or tissue web, in machines for producing and/or processing the same, comprising a flexible roll jacket with a profiled surface for water absorption which, in order to form a pressing nip, is pressed by at least one pressing element having a concave pressing surface against a cylindrical mating roll with a continuous dewatering belt for absorbing the pressed-out water running at least between the shoe press roll and the fibrous web and which is guided off the shoe press roll behind the press nip and in which a water collection device is provided between the shoe press roll and this dewatering belt as close to the press nip as possible for collecting and removing the water spinning off the roll jacket of the shoe press roll.
2. Discussion of Background Information
Such rolls have been known for a long time in which the water pressed-out of the fibrous web is not only absorbed by the dewatering belt but also by the roll jacket. The water adhering to the surface of the profiled roll jacket is spun off and collected behind the press nip. In order to reduce or avoid the remoistening of the dewatering belt, a water collection device is positioned as close as possible to the end of the press nip. Since this is limited for reasons of construction, however, considerable remoistening of the dewatering belt occurs frequently, in particular at high speeds, and thus also particularly leads to an uneven remoistening of the fibrous web. The moisture cross profile worsened hereby has a very negative effect on the entire production process or processing process.
It is therefore an aspect of the invention to counteract the remoistening of the dewatering belt by the spinoff water of the roll jacket.
This aspect was attained according to the invention by connecting a transitional zone to the concavely bent press nip that begins with a convexly bent beginning zone with a relatively large radius and ends in a convexly bent end zone with a relatively small radius. The direction and the amount of the water spinoff of the roll jacket is essentially determined by centrifugal forces. However, the centrifugal force is proportional to the square of the speed and inversely proportional to the bending radius. By designing the transitional zone according to the invention, the centrifugal forces are minimized at the beginning and are enhanced only in the end zone due to the relatively small bending radius. Therefore, the spinning off of the water from the surface of the roll jacket essentially occurs at the end of the transitional zone. As an exceptional case, in particular in shoe press rolls with small roll diameters, the beginning zone can also have an infinitely large radius, i.e., run straight.
Due to the high speed of the machine, the direction of the water spun off in the end zone is essentially between the press jacket and the tangent at the beginning of the end zone. As a result, not only is the beginning of the spin-off of considerable amounts of water pushed away from the end of the press nip, but the direction of the spun-off water is also directed more closely towards the roll jacket and away from the dewatering belt. This again allows the collection of considerable parts of the spun-off water by the water collection device which is embodied in a water channel and, in particular, can also be suctioned by a vacuum connection.
The guidance of the roll jacket occurs behind the press nip via a guidance element, where the pressing element and the guidance element should be lubricated. In order to simplify the construction, it is advantageous to connect the guidance element with the pressing element, preferably embodying them as one piece.
In order to shift the beginning of the spin-off of the water as far away from the press nip as possible in the transitional zone between beginning zone and end zone, at least one convexly bent transitional zone and/or at least one straight transitional zone should be provided. Here, the bending radius of a bent transitional zone that may be present should be considerably larger than that of the end zone. In case of the infinitely large bending radius, the so-called straight transitional zone would be the result.
It can also be advantageous for the bending radius of a convexly bent transitional zone for the lengthening of the transitional zone to be larger, in particular much larger, than that of the beginning zone.
In order to collect and keep as much water as possible, the surface of the roll jacket should be provided with grooves and/or blind bores. These grooves or blind bores relax at the end of the press nip and thus produce an additional suction effect. This suction effect keeps the water at the roll jacket in the bent zone of the beginning zone, therefore, it should be relatively short, preferably considerably shorter than the transitional zone or its sum.
Between the mating roll and the fibrous web, an additional belt, preferably in the form of a dewatering belt, or a transfer belt can be provided for guiding the fibrous web from the mating roll to a subsequent unit. The dewatering belts are generally formed as wires or felts and serve to absorb and remove the water pressed-out in the press nip.
The invention is particularly advantageous in shoe press rolls positioned above the fibrous web since here the gravitational force supports the spin-off of the water towards the fibrous web.
According to an aspect of the present invention, a shoe press roll for dewatering a fibrous web in machines for at least one of producing and processing a fibrous web is provided, including a flexible roll jacket having a profiled surface for water absorption. At least one press element is provided, having a concave pressing surface, arranged against a cylindrical mating roll to form a concavely bent press nip for pressing the flexible roll jacket. A continuous dewatering belt is positioned at least between the shoe press roll and the fibrous web for absorbing pressed-out water, being guided off of the roll jacket after the press nip. A water collection device is arranged for collecting and removing water spinoff from the roll jacket said water collection device being positioned between the shoe press roll and the dewatering belt, and as close as possible behind the press nip, relative to a belt travel direction. A transitional zone is arranged to follow the concavely bent press nip comprising a convexly bent beginning zone, relative to the belt travel direction, with a comparatively large bending radius and with a convexly bent end zone with a comparatively small bending radius.
According to another aspect of the present invention, the roll jacket runs over at least one guidance element in the transitional zone. In another aspect of the present invention, the guidance element is connected to the pressing element. According to a further aspect of the present invention, the guidance element is a one piece design. According to a still further aspect of the present invention, wherein, in the transitional zone between the beginning zone and the end zone, at least one convexly bent transitional zone is provided.
Further aspects of the invention include the bending radius of the at least one convexly bent transitional zone being larger than the bending radius of the end zone. According to other aspects of the present invention the transitional zone between the beginning zone and the end zone is provided with at least one substantially straight transitional zone.
According to another aspect of the present invention, the bending radius of the at least one convexly bent transitional zone is larger than the bending radius of the beginning zone. According to a further aspect of the present invention, a surface of the roll jacket is provided with at least one of grooves and blind bores. According to still a further aspect of the invention, the beginning zone is short. Further aspects of the invention include a beginning zone that is shorter than the transitional zone.
According to an aspect of the invention, the water collection device includes a water channel. According to another aspect of the present invention, the collection device is provided with suction. Additionally, other aspects of the present invention include at least one additional dewatering belt including a dewatering belt or a transitional belt that runs between the fibrous web and the mating roll. In another aspect of the present invention, the dewatering belts can be either felts or wires. According to still a further aspect of the invention the fibrous web is one of a paper web, cardboard web and tissue web.
According to a further aspect of the present invention, the convexly bent beginning zone has a radius greater than about 5 mm. According to another aspect of the present invention, the convexly bent end zone has a radius greater than about 5 mm. In another aspect of the present invention, the transitional zone has a radius greater than about 100 mm. According to still a further aspect of the invention, the web travels at a speed greater than about 300 m/min.
According to an aspect of the invention, a shoe press roll for dewatering a fibrous web is provided including at least one press element, with a flexible roll jacket having a profiled surface for water absorption, the at least one press element forming a concave pressing surface and a transitional zone located next to the concave pressing surface in web travel direction, the transitional zone comprising a convexly bent beginning zone and a convexly bent end zone; a cylindrical mating roll arranged to form a concavely bent press nip with the concave pressing surface of the at least one press element; a continuous dewatering belt positioned at least between the shoe press roll and the fibrous web for absorbing pressed-out water guided off the flexible roll jacket; and a water collection device positioned between the at least one press element and the dewatering belt.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.